Process of producing matrices for the electroforming of foraminous sheet



Aug. 4, 1942. Q. o s 2,291.829

PROCESS OF PRODUCING MATRICES FOR THE ELECTROFORMING OF FORAMINOUS SIIEET Filed 001:. 6, 1939 ATTORNEY cylinder; j Figs. 6, 7, 8, 9, and show further stepsin the Patented Aug. 4, 1942 PROCESS OFaPRODUCING MATRICES FOR THE ELECTROFORMING OF FORAMINOUS SHEET Edward 0. Norris, Westport, Conn.,

Edward 0. Norris, Inc., poration of New York Application October 6, 1939, Serial No. 298,215

3 Claims.

The invention relates to matrice adapted to be employed as a cathode for the electrolytic formation (commonly known as electroforming) of foraminous sheet, and the process of producing them.

In the preferred form, the matrix produced is in the shape of a hollow cylinder, the outer pcriphery of which constitutes'the deposit-receiving 1 surface. The deposit-receiving surface of such a matrix comprises a network of electrically conductive material, or at least of material capable of receiving an electrolytic deposit. The network is usually in the form of a grille, and the spaces delimited by the network are of electrically nonconductive material, or at least of material that is passive to electrolytic. deposition. In matrices of this character the passive areas may be produced by first creating a multitude of'pits or cavities in a metal surface and then filling the pits or cavities with insulating material whichmay be Bakelite, glass, enamel or other material having the required insulating properties, strength, adaptability for easy application, and resistance to corrosion under the action of electrolytes.

The foregoin and various other methods for producing such a matrix are described in my United States Patent No. 2,166,366, issued July 18, 1939, and United States Patent No. 2,166,367, issued July 18, 1989, and, as the details of the method as thus far referred to are not a part of the invention, they will be only briefly described herein.

Referring to the drawing,

'Fig. lis a perspective view of a fragment of a plate in which pits have been formed as above referred to; Fig. 2 is a cross-section of a cylinder the peripheryof which constitutes the deposit-receiving surface. It is to be noted that the pits shown in this figure are on a very much larger scale than that of the cylinder itself;

Fig. 3 is a view in section of the ends of a complete plate as shown in Fig. l, which have been brought around to meet each other preparatory to joining them together to form a cylinder;

Fig. 4 is a view similar to section 3 showing the meeting ends of the plate fastened together with solder;

" Fig. 5 is a view of that Dortion of the cylinder where the joint occurs, which has been reinforced by an additional deposit on the interior of the process;

assignor to complete matrix, but for purposes of clarity it is shown flat, although it is to be assumed in practice that it takes the curvature of the cylinder itself.

Describing the drawing, the plate of which Fig. 1 shows a fragment, is produced by one or another of the methods shown and described in my patents above referred to. Briefly, for exam-- ple, a metal plate (copper, for instance) is coated with a film of light-sensitive material, such as light-sensitized photographer's glue. The lightsensitized surface is then exposed to a beam of light passing through a negative of a standard half-tone screen-i. e., the'negative of a halftone screen in which the crossed lines are opaque to light, while the intermediate areas are transparent to light. The plate is then developed in the usual manner by washin with water, thus leaving adherent bands of partially hardened gelatin exhibiting a reticular pattern with the intermediate areas of metal exposed. By then treating with a suitable etching fluid (for example, ferric chloride in the case of copper), a multitude of pits are created in the surface. The hardened gelatin may then be removed by abrasion, dissolving or any other suitable method. The result is a complete plate the surface of which exhibits the pits l, delimited by the series oi. lands 2, and the series of crossing lands 3.

It is to be assumed that the area of, the plate is suflicient to permit two opposite ends to be in Fig. 2'.

Itshould be now noted that all of the drawings are on a very much more exaggerated scale than is actually used in practice. Further, it. is to be noted that in Fig. 2 the pits are on a very much larger scale than is the cylinder itself. In point of fact, the pits are almost, and in the majority of cases actually are, microscopic in size, there being say anywhere from fifty to several hundred of them per linear inch on the plate itself.

Fig. 3 is a fragment of the cylinder including only that portion showing the ends of the plate after they have been brought around to meet each other. After this has been done, the opposing surfaces of the ends are preferably coated with some material, such as asphaltum 4 which Fig, 11 shows a fragment of the surface of the into abutment as shown in Fig. 4, they are firmly maintained in that relationship by the application of solder 5. Low melting point lead and tin solder will suffice. It should be noted that in practice it is desirable that the ends of the plate be carefully trimmed so that their junction line will run along one of the series of lands. The purpose. as will become apparent, is to produce a matrix in which there will be no break in the continuity or size of the pits in the region of the junction of the ends.

The next step is to mask the outer surface of the cylinder by the application of shellac or other material that will protect it from receiving an electrolytic deposit. The asphaltum 4 is then dissolved off, and a plate of nickel is applied to the interior periphery of the cylinder by electroplating. In carrying out this step the anode is preferably inserted in the interior of the cylinder and positioned according to well-known electroplating principles so that a deposit of uniform depth will result. The results of this step are shown in Fig. 5, wherein the numeral 6 indicates the nickel deposit, and it will be noted that the nickel has been thrown into the gap between the ends of the plate, as indicated at I. It will be obvious that thus far the result is a virtually seamless cylinder with pits uniformly disposed throughout its periphery including the region of the junction of the ends of the plate. The solder should then be removed, which may be done by dissolving it by a strong solution of three-fourths hydrochloric acid and one-fourth acetic acid.

The next step is illustrated by Fig. 6, wherein the walls of the pits have been coated with shellac 8 leaving the lands 2 and 3 exposed. This is accomplished by merely applying the shellac to the'outer periphery of the cylinder, and after it has hardened rubbing off the lands by means of an abrasive, such as pumice. The purpose of applying the shellac is to prevent the adherence of an electrolytic deposit on the walls of the pits, as will be further referred to.

After the shellac has been applied and rubbed off the lands as above described, the cylinder is subjected cathodically to an electroplating step wherein a metal such as nickel 9 is plated on the lands. This step in the process is stopped when the nickel deposit has crept partially over the shellac in the pits, say about half way down as shown in Fig. 7, thus partially blanketing the walls.

After the nickel has been deposited on the lands, as has been Just described, the shellac is carefully washed out of the pits by a suitable solvent such as alcohol, still however leaving the nickel deposit as shown in Fig. 8. The remaining steps in the process are for the purpose of producing a-ridge about the side walls of the pits so that, when insulating material hasbeen inserted in them and allowed to harden. the inserts will be securely locked in place. This result is accomplished by treating the plate 8 with an etching agent which reacts on the copper but not to any appreciable extent on the nickel. A suitable reagent for this purpose is (1) a solution of potassium cyanide in water or preferably (2) a mixture of chromic and sulphuric acids in water, suitable proportions being about as follows:

Neither of these reagents will have any appreciis allowed for the necessary reaction on the copper. The result of this second etching step is to deepen the pits as shown at Ill, and at the same time to undercut the walls of the pits and leave the ridges ll projecting into their interior. While it might be expected that the action of the reagent would take place in the space I! between the overhanging portions of the nickel deposit and the walls of the pits, nevertheless I find that that is not so and ascribe the phenomenon to the fact that the etching reagent rather quickly spends itself in these spaces due to its small volume therein with a consequent diminution in the rate of etching.

After the second etching of the pits, the effect of which is shown in Fig. 9, the nickel is removed by any suitable method such as deplating in a -ab1e effect on the nickel if merely enough'time nickel bathi. e., treating the structure of Fig. 9 anodically in such a bath.

The nickel having been removed, the pits have the appearance of those shown in Fig. 10. These pits may be then filled with Bakelite by squeegeeing, for example, and the surface rubbed off with an abrasive so as to expose the metal of the lands 2 and 3. The appearance of the surface and a section thru a row of pits is illustrated in Fig. 11, wherein the Bakelite fillings are indicated by the numeral l3. The surface in the case of this figure is shown fiat for purposes of clarity. In point of fact, a fragment of the surface including only the number of pits shown in Fig. 11 would be of such a small curvature that it would be substantially flat. The same is true, of course, of the showing of all of the figures, the curvature in all cases being in practice much less than as it appears.

It should be explained that the materials which I have named for producing the matrix are illustrative only-for example, in specifying nickel and copper as the two metals employed in the process, I select them merely because they are cheap and because they are available common etching agents that react on one to the exclusion of the other. As a material for the fillings, Bakelite is selected merely because I have found it preferable to other materials. i It is easily applied, comparatively hard when solidified, very resistant to the action of most electrolytes used in electroforming, and is a good insulator against electrolytic deposition.

I have described above certain embodiments of my invention and a preferred process with certain modifications thereof, but I wish it 'to be understood that these are illustrative and not limitativeof my invention and that I reserve the right to make various changes'in form, construction, and arrangement of parts and also to make various changes in process of manufacture falling within the spirit and scope of my invention, as set forth in the claims.

I claim:

1. In the process of producing a matrix for the electroforming of foraminous sheet, the steps which comprise producing a multitude of pits in the surface of a metal plate, protecting by the applicaton of a resist the walls of the pits for a substantial distance below their orifices and also said unprotected portions until the said pits have been deepened and the unprotected portions of the walls have been undercut, and then filling the said pits with material the exposed surface of which is passive to electrolytic deposition.

2. In the process of producing from a metal plate the surface of which is provided with a multitude oi pits, a matrix for the electroforming of foraminous sheet, the steps which comprise applying by electrodeposition to the lands which delimit the orifices of the pits an adherent electrolytic deposit of material that'isresistant to an etching reagent that has the property of reacting on the material of the plate, continuing the deposit until the same creeps for a. substantial distance down over and partially blankets the walls of the pits, then applying said reagent to the pits until the same are deepened and the walls thereof are undercut, then removing said electrolytic deposit, and then filling the pits with electroforming of foraminous sheet, the steps which comprise producing a multitude of pits in the surface of a copper plate, applying by-electrodeposition a coat of nickel to the lands delimiting the orifices of the pits and allowing the deposit to creep down over and blanket the walls of the pits, and etching the unblanketed portions of the walls of the pits by an etching agent that is passive to nickel until the said pits have been deepened and the unprotected portions of the walls have been undercut, and then filling the said pits with material that is passive to electrolytic deposition.

EDWARD O. NORRIS. 

